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From Maciej Krol,"With advent of GUI applications in OSG there is a growing need to redirect notification messages to third party systems. For example windows applications do not have console output, it would be appropriate to redirect notifications to GUI widget or debug output. I have revamped notification system to fit this need. New notification stream is using NotifyHandler? as a message sink. Handler is called whenever stream is synchronized (i.e. after <<std::endl). Standard streams std::cout and std::cerr are no longer used although by default StandardNotifyHandler? is a message sink. Custom notification handler can be set with osg::setNotifyHandler(NotifyHandler? *) function.

I have seen on osg-users that some people do std::cerr.rdbuf(otherStream.rdbuf()) to redirect notifications. This trick will no longer work since osg::notify() returns internal osg::NotifyStream? not std::cout or std::cerr. You can use osg::notify().rdbuf(otherStream.rdbuf()) to do this instead.

Additionally I've made some minor fixes:
- Minor imrovements to osg::notify documentation
- NullStream? could crash by deleting stream buffer other than default NullStreamBuffer? in the destructor i.e. after osg::notify(osg::DEBUG_FP).rdbuf(otherStream.rdbuf())"